38 replies to this topic

[littlejohny]

Spheres filling a given volume contain about 1/5 empty space, IIRC, so work out how many 1cm balls take up 400ml and you have a good estimate to buy. (I'll save you the time; it's about 764, so 12 packets = $60 worth)

And then they'd be crap anyway. The small size would impact you milling efficiency due to the smaller mass (especially in such a small jar), and the holes would fill up with crap and cross-contaminate batches of comp.

Well I went back into big-W to look at the sinkers I found some more that are about 12-13mm OD size I think I might go with them good thing is they come all in the same size container as the 1cm ones for $4.44. Now that I have looked at the size of the container they come in, they are about the same size as the ID of the PVC and about 2 1/2 inches high, so I think I will still be able to get out of it for $10-$15 for the media.
sorry but I think your math calculations may be wrong

As for cross-contaminating batches of comp I will only be milling KNO3,C,S,and dextrin. This is only a small mill for me to start out with once I get more experience I'll make a bigger one for more complex things.

[maxman]

Can anyone into electronics tell me if this Speed controller would be suitable for a ball mill motor? My motor is .37kw ie 370W 2.1A 240v 50hz single phase.

I think it will but in the catalogue it says "these modules will not accept inductive loads" I thought all motors were inductive loads? Yet this is a motor speed controller

[karlfoxman]

That speed contoller is most prob used to supply DC Motors, it will use Pulse Width Modulation. You should use pulleys to get the correct rpm on your ball mill. Your motor is an AC motor only.

[maxman]

Karl, the pdf file says it is an AC motor controller. My mill doubles up as a tyre star roller. At full speed about 2760 RPM it rotates my 24" tyre at 32RPM but is too fast for a 4" mil jar, spinning it at 200. If I half this withthe speed control then it should be about correct at 100. I already use a 2" to 7" pully

[BrightStar]

Hi maxman, The motor speed controller here looks like it is for ac 'universal motors' only. These are essentially constructed the same as dc motors, usually with brushes / commutators and run asynchronous to the mains supply.

Universal motors are used in power drills, vacuum cleaners etc and are generally noisy, sparky and quite compact. As Karl says, the controller uses PWM chopping the mains supply at 100Hz, which is fine for ac universal motors.

Most larger or continuously rated ac drives are induction motors and are generally more reliable (used in fans, pumps, lathes, ball mills etc...). They are semi-synchronous ac machines and rely on following the phase of the ac power supply. The three-phase variants use three separate windings to create a rotating magnetic field which the rotor can follow. The single-phase versions often have two or more windings internally, some of which are phase delayed with a capacitor or the coil construction. Due to this phase relationship, induction motors cannot be usefully speed controlled with the suggested controller - chopping the supply would probably just create excess heat.

An inverter speed controller can be used (usually with a three-phase motor output, even from a single-phase input) to vary the frequency and voltage of the supply, allowing control of the speed and torque of ac induction motors...

Does this help?

Edited by BrightStar, 23 April 2007 - 09:12 PM.

[maxman]

The motor I have is a capacitor start motor. I think it was used as an industrial pump. It is fully enclosed but it does have brushes and a commutator. No sparking is visable from the brushes. It also has a cooling fan on the back of it.

It look very much like this one Motor

[BrightStar]

That motor looks very similar to mine. It's a single-phase ac induction motor and depends on a clean 50/60Hz ac supply. You can't, at least in theory, speed control it with a simple triac chopper type speed controller - these can only be used for the universal motors found in drills, hair dryers etc...

EDIT: Looks like it might be possible to build a microcontroller based inverter: http://www.designnew...ndustryid=43658

Edited by BrightStar, 08 May 2007 - 07:15 PM.

[BigBang]

That circuit is a triac based speed controller for single phase AC motors. Or in other words a glorified dimmer switch, which you can pick up for about a fiver!

If you are going to go down the dimmer switch road, make sure the dimmer can handle the current drawn by your motor.

Many appliances have these circuits built in and they work very well e.g drills vacuums etc. The only problem with controlling the speed using these circuits, is that the motors have very little torque at low revs.

[dr thrust]

hi got a nice big fat pump motor for free,seems to have lots of wires,poss a 3 phase, ive heard you can wire them to single phase with a delta pattern can anybody throw a bit of light on it cheers???? update! ha cooked it tossed it for a single phase motor of a pillar drill,got it for a fiver of a carboot ,going to strip it down and use the whole head assembly pulleys and all,seems you can change the spindle speed from 2600rpm to 525rpm in four stepped pulleys

Edited by chris m, 12 June 2007 - 05:30 PM.